This invention relates to polymers and, more particularly, to non-ionic graft copolymers that are soluble in aqueous vehicles but are substantially insoluble in water. The graft copolymers are particularly useful as film-forming binders in aqueous dispersions, such as paints or inks, and overcoat compositions.
For many reasons, aqueous dispersions are widely used as coating compositions, such as paints and inks. While these aqueous dispersions have the obvious environmental benefits over their solvent-based counterparts, the aqueous nature of the dispersion creates some unique disadvantages. For instance, the components in an aqueous dispersion need to be soluble or dispersible in the vehicle, which is mostly water. Thus, the coating tends to be sensitive to water or high moisture, which makes it unsuitable for many of its intended applications. To overcome this problem, a class of polymers known as binders has been developed. These binders, when added to the coating composition, are intended to function as film forming agents that effectively bind the various components of the coating together, particularly the pigment particles used in such coatings, as the coating dries or cures. The use of a proper binder can dramatically improve certain properties of the coating, such as resistance to smear, abrasion, water and washing (i.e., detergents).
An additional challenge is presented in selecting binders for ink applications, particularly ink jet inks. Ink jet ink printing is a form of digital printing in which droplets of ink are made to be ejected (i.e., “fire”) from an orifice in a printhead or a spray nozzle in response to an electronic signal from, for example, a computer. Examples of ink jet printing include the thermal ink jet printing, piezoelectric ink jet printing, continuous ink jet printing and air brush printing.
While paints and other coating applications can be in a variety of ways, ink jet inks must be applied by ejecting or jetting small droplets of ink from an orifice in a printhead. In addition, the ink must be formulated such that it will not form a film on the components of the printhead (e.g., resistors used in thermal ink jet printheads), won't puddle on the orifice plate, and won't dry out and clog the openings in the orifice plate. Further, ink jet inks have a much narrower viscosity tolerance than do paints or similar coating applications. Thus, it is far more difficult to formulate ink jet inks as compared to other coatings and, in particular, the requirements of the binder polymer are significantly more demanding. For example, whereas a paint might be formulated to contain 30–40% by weight of a binder polymer, an ink cannot tolerate more than about 20% as a theoretical maximum given the current printhead technology and, in most prior art, the binder content cannot exceed about 2–4% by weight of the ink composition.
In the past decade, ink jet printing, particularly the thermal and piezo forms, has become extremely popular for home office, small office and personal printer applications, primarily due to its relatively low cost, speed and quite operation. In more recent years, the popularity of ink jet printing has increased even further due to the introducing of systems (printers, software, media and inks) offering very high quality (near photographic) color and graphics capabilities. As the capabilities of ink jet technology increase, the use of such technology has expanded into other market segments, such as in large format and very large format applications. In general, the terms “large format” and “very large format” are used to define a class of printers that operate with a particular size media. For example, large format is commonly used to mean printers utilize media of not less than 17 inches in the smallest dimension and very large format is normally used to means printers that utilize media of not less than about 60 inches in the smallest dimension. Such printers are used for applications such as banners, signage, displays, posters, billboards, as well as textile printing applications for clothing, fabrics, draperies and similar applications.
The use of ink jet printing in the large and very larger format applications (for convenience, collectively referred to as “large format”) has important advantages, not the least of which is the savings in short production runs over more traditional analogue printing methods. Yet, there are also disadvantages. For example, the types of final products produced for these applications may be subject to the elements in outdoor usage (e.g., billboad or awning applications), laundering (e.g., clothing applications), abrasive friction (e.g., automobile interior fabrics), etc. and thus need to be far more lightfast, waterfast, washfast and abrasion resistant than typically required for office or home printing applications. While much improvement has been made in enhancing lightfastness and waterfastness of ink jet inks in recent past, due to the use of pigment colorants, there is a need in the art for improving the resistance of ink jet inks to smear, abrasion and washing.